Method and device for non-intrusive measurement of blood pressure in a circuit of a dialysis machine

ABSTRACT

A method for the non-intrusive measurement of blood pressure in a circuit ( 3 ) of a dialysis machine ( 1 ), using a device ( 24 ) provided with a sleeve ( 6 ) forming a portion of the blood circuit ( 3 ) and having at least one part ( 14 ) which moves according to the pressure difference between the inside and the outside of the sleeve ( 6 ), and with an emitter ( 22 ) and a receiver ( 23 ) of electromagnetic waves; the method comprising the emission of a beam of electromagnetic waves and the receiving of a beam of electromagnetic waves reflected from the moving part ( 14 ), in order to measure the displacement of the moving part ( 14 ) in such a way as to establish a relationship between the position of the moving part ( 14 ) and the pressure of the blood circulating in the sleeve ( 6 ).

[0001] The present invention relates to a method for the non-intrusivemeasurement of blood pressure in a circuit of a dialysis machine.

[0002] A dialysis machine of the known type comprises a machine casing,to which are connected a first circuit for blood circulation and asecond circuit for the circulation of dialysate. The first and secondcircuits are connected to a filter so that the blood and the dialysaterespectively can be directed through the filter, which is provided witha semi-permeable membrane which, when in use, separates the blood fromthe dialysate.

[0003] There is a known way of measuring blood pressure in anon-intrusive way in the first circuit of a machine of this type, bymeans of a measuring device having a sleeve which forms a portion of thefirst circuit and comprises a membrane which is elastic, and thereforesensitive to the pressure of the blood circulating in the sleeve, and asensor fitted on the machine casing. In a first method of non-intrusivemeasurement of the blood pressure, the sleeve is fixed to the machine atthe position of the sensor in such a way as to form a sealed chamber,inside which the aforesaid sensor is located in order to directlymeasure the pressure of the air contained in the sealed chamber and,consequently, the blood pressure. This method provides a satisfactorymeasurement of the blood pressure and can measure pressures which areeither positive or negative, in other words below the ambient pressure.However, this method has the disadvantages of requiring a precisefitting of the sleeve in the housing and the maintenance of the sealingof the chamber throughout the dialysis treatment.

[0004] To overcome this drawback, an alternative method proposes themeasurement of the force exerted on the membrane by the blood. Toimplement the aforesaid method of non-intrusive measurement of the bloodpressure, it is necessary to use a device comprising a force sensor anda force transmitter positioned in a housing in the machine. The sleeveis coupled to the aforesaid housing in such a way that the forcetransmitter is placed between the force sensor and the membrane, and isin direct contact with both the force sensor and the membrane. Thismethod does not require the formation of a sealed chamber, but cannotprovide negative pressure values.

[0005] In order to measure negative pressure values, the membrane ispre-compressed against the force transmitter while the sleeve is beingconnected to the machine. However, the degree of pre-compression isaffected by play in the connection, which can give rise topre-compression errors and consequent measurement errors.

[0006] An alternative method of measuring negative pressure valuesconsists in connecting the membrane to the force transmitter, forexample by means of a magnet integral with the membrane. However, thisprocedure also has drawbacks, since it complicates the membrane and thesensor, which has to operate in tension and not only in compression.

[0007] The object of the present invention is to provide a method forthe non-intrusive measurement of the blood pressure in a circuit of adialysis machine, which overcomes the drawbacks of the known art, andwhich, at the same time, provides accurate measurements of the pressureand is simple to manufacture and use.

[0008] According to the present invention, a method is provided for thenon-intrusive measurement of the blood pressure in a circuit of adialysis machine, by means of a sleeve forming a portion of the saidcircuit and comprising a part which moves according to the pressuredifference between the inside and the outside of the sleeve, the methodbeing characterized in that a beam of electromagnetic waves is directedtowards the said moving portion and the beam reflected from the saidmoving portion is received to determine the displacement of the movingportion with respect to a reference position of the moving portion.

[0009] The present invention also relates to a device.

[0010] According to the present invention, a device is provided for thenon-intrusive measurement of the blood pressure in a circuit of adialysis machine, the device comprising a sleeve provided with a partwhich moves according to the pressure difference between the inside andthe outside of the sleeve, the device being characterized in that itcomprises an emitter of a beam of electromagnetic waves and a receiverof a beam of electromagnetic waves reflected from the moving part tomeasure the displacements of the said moving part with respect to areference position of the moving part.

[0011] The present invention will now be described with reference to theattached drawings, which show a non-restrictive example of embodiment inwhich

[0012]FIG. 1 is a perspective view, with parts removed for clarity, of adialysis machine comprising a device for implementing the methodaccording to the present invention;

[0013]FIG. 2 is a lateral elevation, with parts removed for clarity andon an enlarged scale, of a detail of a circuit associated with themachine of FIG. 1; and

[0014]FIG. 3 is a schematic sectional view, on an enlarged scale andwith parts removed for clarity, of the detail of the circuit of FIG. 2associated with the machine of FIG. 1.

[0015] With reference to FIG. 1, the number 1 indicates the whole of adialysis machine comprising a machine casing 2 and a blood circuit 3(illustrated only partially) which can be connected to the machinecasing 2. The machine 1 can extract blood from a patient, carry out adialysis treatment, and transfer the treated blood to the patient. Thecircuit 3 comprises tubes 4 made from transparent flexible material(generally PVC), and a box 5 made from rigid plastic material,comprising two sleeves 6.

[0016] Each sleeve 6 is connected to two tubes 4 of the circuit 3 insuch a way that the sleeve 6 forms a portion of the circuit 3. One ofthe sleeves 6 is also connected to a tube 7 which is bent into a U-shapeand can interact with a rotor 8 associated with the machine 1 to form aperistaltic pump.

[0017] The machine casing 2 comprises, in addition to the rotor 8, aprocessing and control unit 9, and a mounting 10 for fixing the box 5,sensors 11 being fitted in this mounting.

[0018] With reference to FIG. 2, the box 5 is made, for example, frompolycarbonate or polypropylene or other plastic material. Each sleeve 6forms an internal compartment in the form of a parallelepiped and has awall 12, which has two essentially rigid parts 13 and 14 and a flexiblepart 15 for connection between the portions 13 and 14. With reference toFIG. 3, the parts 13, 14 and 15 are made from the same material, buthave different thicknesses. The part 13 is integral with the remainingparts of the sleeve 6 and is therefore referred to as fixed; it has aconstant thickness, and is essentially rigid. The part 14 is referred toas moving, since it can be displaced with respect to the part 13 and hasa circular shape and essentially the same thickness as the part 13, andis essentially rigid. The part 15 is very thin by comparison with thethickness of parts 13 and 14, and has an annular shape, concentric withthe part 14. The part 15 also has a corrugated profile to permit thedeformation of the part 14 with respect to the part 13. The part 14 hasan inner face 16 and an outer face 17, which, when in use, interactswith one of the sensors 11.

[0019] With reference to FIGS. 1 and 3, each mounting 10 is formed by afixing plate 18 for fixing the box 5 in a known way which is notillustrated in the attached figures, and for placing the box 5 in aspecified position with respect to the machine casing 2. The plate 18has two circular apertures 19 for access to corresponding recesses 20,within which the corresponding sensors 11 are housed. With reference toFIG. 3, each part 14 is positioned before a corresponding aperture 19during the connection of the box 5 to the plate 18, in such a way as tocover a corresponding recess 20.

[0020] Each recess 20 has an axis A which is perpendicular to the plate18 and consequently perpendicular to the face 17, and two walls 21 a and21 b which are inclined with respect to the axis A. Each sensor 11comprises an emitter 22, which is positioned on the wall 21 a and isorientated in such a way as to direct a beam of electromagnetic wavestowards the face 17 at an angle α of inclination with respect to theface 17, and a receiver 23, which is positioned on the wall 21 b toreceive a reflected beam of electromagnetic waves, which forms an angleα with respect to the face 17 on the opposite side to the emitted beam.The position of the reflected beam and, consequently, the area ofincidence of the reflected beam on the receiver 23 are modified by theposition of the face 17 of the portion 14 as shown in broken lines andin chained lines in FIG. 3.

[0021] In practice, each sleeve 6 and each sensor 11 jointly form adevice 24 for measuring the position of the part 14 with respect to thepart 13, and consequently the blood pressure in the circuit 3.

[0022] For this purpose, the receiver 23 is formed from a sequence ofadjacent cells 25, each of which sends a signal when struck by thereflected beam. In the described embodiment, the electromagnetic wavesare in the visible range and the cells are photosensitive cells 25. Theemitter 22 and the receiver 23 are controlled by the unit 9, whichprocesses the signals received from the receiver 23 to determine a valueof blood pressure.

[0023] In use, the box 5 is fixed on the mounting 18 so that the parts14 are positioned before the apertures 19 of the plate 18, as describedabove. Before the dialysis treatment is started, in other words when thecircuit 3 is empty, a procedure of zero setting the measuring device 24is carried out. This zero setting procedure consists in emitting a beamof electromagnetic waves by means of the emitter 22 and determiningwhich cell 25 has received the reflected beam in the rest condition, insuch a way that the unit 9 determines a match between the cell 25 whichhas received the reflected beam and the ambient pressure. In practice,in the zero setting stage, the pressure acting on the face 17 is equalto the pressure acting on the face 16, and the part 14 is in a restposition which is taken as the reference position of the portion 14. Thedialysis treatment is then started, and during the treatment the bloodflows through the circuit 3 and undergoes fluctuations of pressure,according to the operating conditions of the machine 1 and thecharacteristics of the patient, the pressure acting on the face 16 tocause displacements of the part 14 of the wall 12 with respect to thereference position. For example, in FIG. 3, the position of the face 17of the wall 14 is indicated by a broken line, corresponding to anoperating condition in which the blood in the circuit 3 has a pressuregreater than the ambient pressure. In this stage, the point of incidenceof the emitted beam along the outer face 17 moves closer to the emitter22, and consequently the reflected beam shown in broken lines strikes adifferent photosensitive cell 25 from the cell 25 which is struck whenthe part 14 is in the reference position. The unit 9 receives the signalfrom the struck cell 25 and determines the blood pressure in accordancewith a calibration carried out by an experimental procedure.

[0024] Similarly, when the blood circulating in the circuit 3 has apressure below the ambient pressure, the face 17 assumes the positionindicated by a chained line in FIG. 3, and is further away from theemitter 22 than it is in the rest condition. Consequently, the reflectedbeam is directed towards a photosensitive cell 25 which measures the newposition of the face 17 and the unit 9 determines a corresponding valueof blood pressure.

[0025] The described device 24 has the advantage of requiring relativelysimple fitting and allows errors of fitting to be correctedautomatically, by means of the zero setting procedure.

1) Method for the non-intrusive measurement of blood pressure in a circuit (3) of a dialysis machine (1), by means of a sleeve (6) forming a portion of the said circuit (3) and comprising a part (14) which moves according to the pressure difference between the inside and the outside of the sleeve (6), the method being characterized in that a beam of electromagnetic waves is directed towards the said moving part (14) and the beam reflected from the said moving part (14) is received in order to determine the displacement of the moving part (14) with respect to a reference position of the moving part (14). 2) Method according to claim 1, characterized in that the electromagnetic waves are in the visible spectrum. 3) Method according to claim 1 or 2, characterized in that the said emitter (22) and the said receiver (23) are located on the dialysis machine (1). 4) Method according to any one of the preceding claims, characterized in that the emitted beam is directed in such a way that the said emitted beam is inclined with respect to an outer face (17) of the said moving part (14). 5) Method according to claim 4, characterized in that the said part is rigid and has an inner face (16) which can be placed in contact with the blood circulating in the said circuit (3). 6) Method according to claim 4 or 5, characterized in that the said receiver (23) comprises a sequence of cells (25) sensitive to the electromagnetic waves. 7) Method according claim 5, characterized in that it comprises a zero setting stage, in which the said reference position of the moving part (14) with respect to the emitter (22) is determined, the said stage of zero setting comprising the association of at least one sensitive cell (25) of the receiver (23) with a known value of pressure within the sleeve (6); the said reference position being determined for an operating condition in which the pressure acting on the outer face (17) is equal to the pressure acting on the inner face (16). 8) Method according to claim 7, characterized in that the said pressure is the ambient pressure; the said stage of zero setting being implemented before the start of the dialysis treatment. 9) Device for the non-intrusive measurement of blood pressure in a circuit (3) of a dialysis machine (1), the device (24) comprising a sleeve (6) provided with a part (14) which moves according to the pressure difference between the inside and the outside of the sleeve (6), the device being characterized in that it comprises an emitter (22) of a beam of electromagnetic waves and a receiver (23) of a beam of electromagnetic waves reflected from the moving part (14) to measure the displacements of the said moving part (14) with respect to a reference position of the moving part (14). 10) Device according to claim 9, characterized in that the emitter (22) and the receiver (23) are fitted on the dialysis machine (1) in a mounting (10) for receiving the said sleeve (6). 11) Device according to claim 9 or 10, characterized in that the said moving part (14) is a rigid part of a wall (12) of the said sleeve (6). 12) Device according to claim 11, characterized in that the said part has an inner face (16) which can be placed in contact with the blood flowing within the circuit (3) and an outer face (17) which can reflect the emitted beam. 13) Device according to claim 9 or 11, characterized in that the wall (12) comprises a rigid fixed part (13), the said moving part (14) and a flexible part (15) for connecting the said part (14) to the said fixed part (13). 14) Device according to claim 13, characterized in that the fixed part (13), the moving part (14) and the flexible part (15) are made in one piece and from the same material. 15) Device according to claim 14, characterized in that the flexible part (15) is thinner than the thickness of the fixed part (13) and the moving part (15). 16) Device according to claim 15, characterized in that the said moving part (14) is circular, the said flexible part (15) being annular and concentric with the moving part (14). 17) Device according to claim 16, characterized in that the said flexible part (15) is corrugated. 